doc asked
I have received a false positive for marijuana from a doctor testing me because I use hydrocodone. But I do not use it so my medication has been cut off. I am in severe pain for degenerative disc disorder in my spine. I do use high doses of ibuprofen from the same doctor. Don't know what has put me in this position.
Answer
Many different over the counter and prescription medications have been reported to cause false positives for marijuana (specifically THC metabolites) on urine drug tests. Studies have shown that commonly used over the counter medications, such as Advil (ibuprofen), have the potential to cause unexpected results.
Marijuana Drug Test False Positives
Although marijuana contains hundreds of compounds, drug screenings generally test for the THC metabolite delta-9-tetrahydrocannabinol-9-carboxylic acid. The following medications have been reported to cause false positives:
- NSAIDs (Non-Steroidal Anti-Inflammatory Drugs): Commonly used NSAIDs include Advil (ibuprofen), Aleve (naproxen), diclofenac, Mobic (meloxicam) and Celebrex. NSAIDs are some of the most often used over the counter pain medications.
- Efavirenz: Efavirenz is an anti-retroviral medication used to treat HIV/AIDS.
- PPIs (Proton Pump Inhibitors): Commonly used PPIs include Prilosec (omeprazole), Prevacid (esomeprazole), Zegerid (omeprazole/sodium bicarbonate) and Protonix (pantoprazole).
How Drug Tests Work And False Positives
As drug tests are often used in pre-employment screenings and medical settings, there is a demand for simple testing methods and fast results. The most commonly used drug tests are urine based immunoassay tests and unfortunately, they are subject to false positives meaning they can show a positive reading for a drug that is not present in a sample.
Common immunoassay tests include the EIA (Enzyme Linked Immunoassay) test and the CEDIA (Closed Enzyme Donor Immunoassay) test, which both use similar principles. They work by utilizing antibodies to react to specific drug compounds. When a drug compound is present in a test sample, an antibody binds to it, which produces a reaction. When a reaction occurs, it is classified as 'positive' result.
Unfortunately, immunoassay based tests have a significant problem with 'cross-reactivity', where drugs that are NOT being tested for react with the wrong antibody (i.e. 'cross react'), which results in a "false-positive". This may have happened in your case, especially since NSAIDs like ibuprofen have been shown to be responsible for marijuana false-positives.
In fact, one study found that ibuprofen caused a false-positive on a marijuana drug test in two subjects after just one days use of ibuprofen.
If you get an unexpected result on a drug test, it is important to inquire about the possibility of a more accurate, confirmatory test that can actually identify specific molecules and don't use antibodies. Such tests include gas or liquid chromatography with mass spectrometry.
Additional Information
In those that do use marijuana, detection times vary widely by individual and usage history. One time use of marijuana can generally be detected for 3 to 7 days on urine tests while consistent use can lead to an individual testing positive for over 30 days after last use.
